Earlier quoted context omitted.
They're known to be fairly accurate prior to 1960, to the best of our knowledge. This is a scientific thing This sounds backwards. We calibrate against the instrumental record up to 1960, we know that there is increasing divergence post 1960, thus should we presume we can have greater trust for the previous eras where we have no instrumental record? Wouldn't the onus be on explaining the divergence? I haven't seen an…
Absolutely. I'm not very good at finding information in scientific papers, but here's the first few I found with Google. If those don't satisfy you, I'll see what I can find when I get home from work. http://www.ldeo.columbia.edu/res/fac/trl/downloads/Publicati... (PDF) is a paper that specifically addresses a lot of the concerns about temperature prediction using tree rings. In particular, I'd like to quote the foll…
there is a substantial amount of overlap between these reconstructions and our actual instrumental record during the calibration period
From memory, I don't think this is quite the right conclusion. Rather, the instrumental record is used to calibrate the reconstruction, so the overlap approaches 100%. Worse, the accusations are that the correlation is even better because any trees not matching the temperature record have been eliminated as non-performing! I don't think either of these papers shows accuracy of reconstruction on an out-of-sample set for which there exists an outside measurement. I'll recheck, though.
None of this really changes what the comment says, which was basically "Don't use this to plot past 1960, because we know that part needs corrections".
I don't disagree here. In the absence of some overriding context, that seems like a valid reading of the comment.